The technology called pedestrian dead reckoning (PDR) has been researched and developed. According to the pedestrian dead reckoning, (i) a moving body, which is a pedestrian, holds or is equipped with a sensor module that includes an (three-axis) acceleration vector sensor and an (three-axis) angular velocity vector sensor (i.e. the sensor module is what is known as a six-axis sensor) and then (ii) a location and an attitude of the pedestrian is estimated based on an acceleration vector and an angular velocity vector which have been obtained by use of the sensor module (see, for example, Non-Patent Literature 1).
Unlike GPS (Global Positioning System) and other positioning technologies that employ wireless signals, PDR is an autonomous tracking technology in which a self-contained sensor is used. This allows the PDR to have such an advantage as being able to make a measurement even without using a special infrastructure (e.g. GPS satellite) for the measurement.
However, according to PDR, slight errors in estimating an attitude (particularly yaw azimuth) generally accumulate. This poses a problem that an error in positioning may increase in proportion to a distance for which a pedestrian has walked.
(Factors in Positioning Errors)
Of factors contributing to an increase in positioning errors, a factor considered as the greatest contributor is an error in estimating, by time integration of an angular velocity vector, an attitude angle (particularly yaw azimuth).
For example, an output from an (three-axis) angular velocity (gyro) sensor includes not only an angular velocity output component but also a zero-point offset (also called bias component). A zero-point offset is an error component that is outputted while a value of zero should be outputted.
Error components such as zero-point offsets are integrated over time, and are accumulated as errors in estimating an attitude. Of such errors, particularly integration errors of bias components of an angular velocity around a gravity axis appear as errors in an azimuth (yaw azimuth).
Therefore, there have been technologies proposed for making calibration of the error component.
For example, Patent Literature 1 discloses a server device configured such that, in a case where a moving body terminal moves from a first location to a second location which causes an amount of errors in location or angle to be a specific amount, a zero-point offset is calculated based on a difference between (i) the location or the angle obtained at the second location with the use of an output of a motion sensor and (ii) the specific amount, which difference is recognized by dead reckoning.